I'm sure 150 is a wrong weight, a typo. I don't have a local source fight report, but non-local would surely mention if there was a 24 pounds difference between the two, but it only mentions Miske heavyweight, Greb middleweight.
The point is even you find a couple more fights where he weighed under middleweight limit, I'm absolutely sure I could find weights for several more key fights where he weighed above 160lb (because in the 1920's Greb didn't train down to below 160lb unless it was a middleweight title fight).

The 150 is probably more realistically 160. It would make more sense.

I don't doubt at all that some (probably most) of the key fights with unlisted weights would have been fought above the middleweight limit, but I also think a fair amount would be at 160 or so, give or take a pound or two. As such, Greb as a middleweight amounts to more than a perpetual loser to Tiger Flowers with one win over a welterweight.